Outline

Objective

Postoperative hyperopia is a frequent result of cataract surgery in eyes after previous keratorefractive surgery. One reason for the underestimation of intraocular lens (IOL) power is the wrong corneal refractive power measurement obtained by keratometers and corneal topography systems after LASIK. The aim of this study was to compare the precision of measurements of three different keratometers after LASIK.

Methods

We measured 58 eyes of 34 refractive patients aged between 20 and 51 years. The preoperative measurements and the measurements one month after the corneal refractive surgery were performed with the Zeiss-Keratometer, the cornea scan (EyeSys Technologies) and the IOL-Master (Zeiss). We compared our measurement results with the results obtained utilizing the clinical history method, i.e. subtraction of the spherical equivalent change after refractive surgery from the original central corneal power - Chm.

Results

The smallest deviation (1.5%) was achieved with the IOL-Master (mean Â± SD: 38.94 D Â± 1.88, vs. Chm: 38.35 D Â± 2.13), which was the exactest of the three keratometers. The Zeiss-Keratometer displayed a deviation of 2% (39.12 D Â± 1.76, Chm: 38.34 D Â± 2.07). The largest deviation (2.5%) was shown with the cornea scan (mean value 39.84 D Â± 1.85, mean value Chm: 38.86 D Â± 2.10), which measured in mean one diopter higher than what was obtained utilizing the Chm. A positive correlation between corrected myopia and the postoperative difference between the measured and calculated value for each keratometer was found.

Conclusions

This study demonstrates that with common keratometers central corneal power is measured to high after LASIK. Because of this, it is very important to have an exact preoperative documentation of keratometry with two different keratometers and to calculate the effective corrected refraction in each patient. Only with these data it is possible to individually calculate the appropriate power of the intraocular lens in the case of necessary cataract surgery.